Business Proposal was the first Kdrama I watched and I'm really glad it was my first. It set the tone and my expectations for all dramas moving forward.

Things I loved:
The chemistry between the ML and FL
The script / dialogue
The humor (I laughed out loud often)
The direction
The second romance story

Things I didn't love:
The mother character was over the top and got on my nerves; I ended up fast-forwarding many of the scenes she was in
The kisses between ML and FL didn't feel realistic EXCEPT for in one scene (you'll know it when you see it). Otherwise, they lacked passion / felt very, very neutered. But ultimately (now, all these months and Kdramas later) I'm glad I saw Business Proposal first and my (low) expectations were set for kisses / physical affection in Kdramas. It's been a nice surprise whenever a Kdrama has a realistic / passionate kiss scene because I always expect them to be neutered and lackluster.

On that note, if you're looking for Kdramas with realistic romance (i.e. passionate kisses) here's my list so far:
The Red Sleeve (or any romance with Lee Se Young, she's incredible; also, this romance is SOOOOOOOO GOOOOOOOD)
Healer (or any romance with Ji Chang Wook)
Goblin (or any romance with Gong Yoo, esp Coffee Prince)
What's Wrong with Secretary Kim (or almost any romance with either Park Min Young OR Park Seo Joon)
Doona
Do You Like Brahams?
Strong Woman Do Bong Soon
Alchemy of Souls Part 2